The prevalence of silent HIV infection in a cohort of individuals at risk for HIV infection (IVDUs and spouses) is being analyzed by PCR and a cell proliferation assay based on the release of cytokines in the early phase of infection with the virus. PCR is being performed on DNA isolated from peripheral blood mononuclear cells and on RNA from serum. The primers used for amplification are the SK 38/39 and SK 145/431. Preliminary results indicate that there is a low but definite incidence of HIV infection in these high risk individuals (3/37 positive by PCR). All of these individuals have been negative for RNA in serum analyzed by PCR.